1. Field of the Invention
The present invention relates to a pressure container and a pressure accumulating/buffer apparatus such as an accumulator which are used in an automobile and an industrial machine, and particularly relates to them where a welded portion between an end plate and a body portion is uniform.
2. Description of the Related Art
Accumulators (pressure accumulating/buffer apparatus) are used in hydraulic circuits and shock absorbers of hydraulic control apparatuses. In the accumulators, insides of pressure containers are generally divided into gas chambers and oil chambers by bellows, and pressure fluctuation in oil flowing into the oil chambers are buffered by the swell/shrink function of gas in the gas chambers due to expansion/shrinkage of the bellows (see Jpn. Pat. Appln. KOKAI Publication Nos. 2001-116002, 2001-116003 and 2003-120601). The accumulators are widely used as apparatuses, that effectively suppress pulsation generated in the coil flowing in the hydraulic circuits, for example, in automobiles and industrial machines.
In order to form pressure containers, it is necessary to joint a contour member to a cover body that closes the contour member with large strength. For example, resistance welding can be used in a pressure container with small thickness (2 mm or less), for example. FIGS. 5 and 6 are diagrams illustrating examples of such pressure containers. That is to say, a pressure container 10 has a steel pipe (contour member) 11, and an end plate 12 that covers an opening of the steel pipe 11. In FIG. 5, 13 and 14 designate electrodes.
In the case where the resistance welding is carried out, an outside surface of the steel pipe 11 is clamped by a double-split electrode 13, an outside surface of the end plate 12 is inserted into the steel pipe 11 from an end side so as to come in contact with its inner wall surface, and the electrode 14 is brought into contact with the outside surface of the steel pipe 11. Meanwhile, the electrode 14 is allowed to touch an upper surface of the end plate 12. While a load is applied to between the electrodes 13 and 14, an electric current is allowed to flow in the electrode 13, the steel pipe 11, the end plate 12 and the electrode 14, so that the inner wall surface of the steel pipe 11 and the outside surface of the end plate 12 are resistance-welded.
On the other hand, in a pressure container with large thickness (2 mm or more) shown in FIG. 7, the outer peripheral surface is jointed by Co2 welding, TIG welding and the like (see F in FIG. 7). FIG. 7 is a diagram illustrating one example of the accumulator. That is to say, an accumulator 20 has a cylindrical shell (contour member) 21, a first end plate (cover body) 22 which is fitted into one opening of the shell 21, and a second end plate (cover body) 23 which is fitted into the other opening. The first end plate 22 is formed with a through hole 22a, and the through hole 22a is blocked by a gas sealing stopper 22b airtightly. Further, the second end plate 23 is formed with a port 23a, and the port 23a is connected to the hydraulic circuit or the like so that oil freely goes in and out the port 23a. 
On a lower surface of the first end plate 22 in FIG. 7, a disc-shaped bellows cap 25 is provided via a metallic bellows 24 so as to be slidably along an axial direction of the shell 21. 26 in FIG. 7 designates a guide attached to an outer peripheral portion of the bellows cap 25. The guide 26 has a function that assists the sliding of the bellows cap 25. A space formed by the first end plate 22, the metallic bellows 24 and the bellows cap 25 is a gas chamber G, and nitrogen gas or the like is sealed thereinto. Further, an oil chamber L is formed between the second end plate 23 and the bellows cap 25.
The above-mentioned method of jointing the pressure container has the following problem. That is to say, in the resistance welding, since the steel pipe is clamped by the double-split electrode, uniform contact and a strong clamping force cannot be obtained, and thus this method can be used only for thin steel pipes with thickness of up to about 2 mm. Further, in the case of the thick steel pipes, in order to obtain the strength of the welded portion by CO2 welding, TIG welding and the like of the outer peripheral surface, the steel pipes become large and heavy.